Stabilization of polyamides



United States Patent 3,384,615 STABELIZATION 0F POLYAMIDES Elias R. Agouri, Pnu, France, and Helmut Miiller, Binningen, Switzerland, assignors to W. R. Grace & (10., New York, N.Y., a corporation of Connecticut No Drawing. Filed May 16, 1966, Ser. No. 559,364 Claims. (Cl. 260-459) This invention relates to the heat stabilization of synthetic, amorphous, linear, transparent polyamides of terephthalic acid, iosphthalic acid, or a mixture of these acids. These polyamides are disclosed in U.S. Patent Nos. 3,150,113, 3,198,771, 3,150,117, 3,145,193 and British Patent Nos. 977,868, and 987,962.

The polyamides of U.S. Patent No. 3,150,117 are linear, amorphous, transparent, film-forming polyamides of terephthalic acid, isophthalic acid and mixtures of these acids and an alkyl-substituted hexaimet'hylenediamine wherein the main hydrocarbon chain contains at least three side chain carbon atoms in the form of one or more alkyl groups. Suitable substituted hexamethylenediamines are, for example, 2-methyl-4-ethylhexamethylenediamine; 2- ethyl 4 methylhexamethylenediamine; 2,2,4-trimethylhexamethylenediamine; 2,4,4 trimethylhexamethylenediamine; 2,2,5,5-tetramethylhexamethylenediamine; 3-isopropylhexamet-hylenediarnine; 3-isooctylhexameth"ylenediamine; 3-isododecylhexamethylenediamine and 2,4-diethylhexamethylenediamine.

US. Patent No. 3,198,771 discloses a synthetic, amorhous, linear, transparent polyamide formed from terephthalic acid, isophthalic acid and mixtures of these acids and a diamine having an alkyl-substituted saturated hydrocarbon chain 6 to carbon atoms in length in which the alkyl substituent consists of one ethyl group.

In U.S. Patent No. 3,145,193, the amorphous polyamide is formed from an acid mixture comprised of terephthalic acid and isophthalic acid and a diamine having an alkyl-substituted saturated hydrocarbon chain 7 to 10 carbon atoms in length with up to 18 carbon atoms in one or more side chains introduced by the alkyl substitution of the main hydrocarbon chain. Suitable alkyl-suhstituted diamines are, for example, Z-methyl-4-ethylheptamethylenediamine; 2-ethyl-4-methylheptamethylenediamine; 2,2, 5,5-tetramethylheptamethylenediamine; 3-isopropylheptamethylenediamine; 3-isooctylheptamethylenediamine; 3,3, 5 trimet'hyloctamethylenediamine; and 2,4-dietnyloctamethylenediamine.

U.S. Patent No. 3,150,113 disclose a transparent polyamide formed from terephthalic acid an a mixture of 3- methyland Z-methyl-hexamethylenediarnine.

In Britsh Patent No. 987,962 a glass clear polyamide is formed from terephthalic acid, isophthalic acid and mixtures thereof, and a mixture of aliphatic diamines. The diarnine mixture is comprised of about 95 to 70 percent by weight of a substituted polyzmethylene diamine having a straight hydrocarbon chain of at least 6 carbon atoms, said straight chain being substituted by at least one alkyl group, the total number of side chain carbon atoms introduced by alkyl substitution being at least 3, and about 5 to percent by weight of an unsubstituted polymethylene diamine of the same chain length. Preferably, the substituted diamine is 2,2,4-trimethylhexamethylenediamine, 2,4,4-trimethylhexamethylenediamine or mixtures of these isomeric diamines, and the unsubstituted polymethylene diamine is hexamethylenediamine.

British Patent No. 977,868, discloses a polyamide formed from 3-amino-methyl-3,5,S-trimethyl-cyclohexylamine and an acid mixture comprised of adipic acid and tercpht'halic acid or isophthalic acid or mixtures thereof.

The invention provides a method of heat-stabilizing polyamides of the aforesaid kind which, unlike known 3,384,615 Patented May 21, 1968 ice processes, does not adversely affect the color or clarity of the polymer, and which is also without adverse effect on the moldability and solubility of the polyarnides.

According to the present invention, a heat-stabilized polyamide composition comprises a synthetic, linear, amorphous polyamide such as those defined above, an alkyl-substituted diphenylamine, a phosphorous acid or salt or ester thereof, and a hydrogen, alkali metal, or alkaline earth metal chloride, bromide or iodide.

The alkyl-substituted diphenylamine has at least one alkyl substituent on each phenyl group. Generally, the alkyl substituents contain 4 to 12 carbon atoms each. Preferably, the alkyl-substituted diphenylamine is the reaction produet of diphenylamine and diisobutylene (Octamine). Octamine is a light brown granular waxy solid having a specific gravity of 0.99 and a melting range of to C. It is soluble in gasoline, benzene, ethylene dichloride and acetone, but insoluble in water. It is believed to be a mixture of C alkylated diphenylamines having the following formula:

H S 17)n where n is 1, 2 or 3. Other suitable alkylated diphenylamines include di-t-butyldiphenylamine, di-neopentyldiphenylamine, and di-isododecyldiphenylamine.

The alkyl-substituted diphenylamine can be used in an amount ranging from 0.1 to 1.0%, preferably 0.2 to 0.5% by weight, of the polyamide. Generally, use of the alkyl-substituted diphenylamine in an amount higher than 1.0% by weight of the polyamide has little beneficial efiect.

The phosphorous compound is preferably phosphorous acid (H PO itself but may also be, for example, sodium or potassium phosphite or hyphosphite or a tri(alkyl) phosphite, e.g. triethyl phosphite or tri isooctyl phosphite. The proportion of the phosphorous compound is generally from 0.02 to 1%, preferably 0.05 to 0.3%, by weight of the polyamide.

The halide constituent is preferably an iodide, especially sodium, calcium, or more particularly, potassium iodide. About 0.01 to 0.1%, preferably 0.02 to 0.06%, by weight of the polyamide should ordinarily be used. More than 0.1% by weight of the halide is liable adversely to effect the transparency of the polyamide.

The three stabilizing ingredients are most conveniently incorporated in the polyamide by mixing with the starting materials used in the polycondensation, and then carrying out the polycondensation in the known manner. It is also possible, however, to incorporate the three stabilizing ingredients in the polyamide by melting the latter and thoroughly mixing in the ingredients using conventional techniques for dispersing solids in molten polymers.

The following examples illustrate the invention. Parts and percentages are by weight unless otherwise indicated.

Example 1 16.6 parts of terephthalic acid were mixed with 30 parts of water and brought almost to boiling on a steam bath. Using a dropping funnel, a solution of 16.5 parts of a mixture of 2,2,4- and 2,4,4 trimethylhexamethylene diamine in 50 parts of ethanol were added slowly dropwise. When all the diamine had been added, the terephthalic acid dissolved. After cooling, the mixed diamine terephthalate salts crystallized out.

A mixture of 300 parts of the salt thus obtained, parts of water, 0.9 part of Octamine, 0.12 part of potassium iodide, 0.33 part of phosphorous acid, and 0.5 part of glacial acetic acid, was heated to C. with constant stirring in an autoclave in the absence of air. The

temperature of the mixture was raised and water vapor vented to reduce the pressure in the autoclave until the mixture reached 250 C. and atmospheric pressure. The mixture, now substantially free from water, was heated to 280 C. over a period of 3 /2 hours and then held at Patent No. 3,150,117) was stabilized with 0.5% of Octamine, 0.05% of potassium bromide and 0.1% of triisooctyl phosphite. After 9 weeks exposure at 130 C., the elongation and tensile strength of the injection-molded dumbbell remained practically unaltered. The oxygen this temperature for a further two hours. The polymer uptake, measured as described in Example 1, was 1.2 melt obtained was extruded into cold water to form rods. cm. per gram. Injection-molded plates, 3 mm. thick, The solid polymer was transparent and glass clear. It were clear and only slightly discolored (yellowish) after melted over a range of 190 C. to 220 C. and had an the 9 weeks heating, whereas the unstabilized polymer intrinsic viscosity of 1.50. Part of the polyarnide was 10 turned dark brown during the same period under the cut into chips and injection-molded to form dumbbel same conditions. shaped test pieces 1 x 2 mm. in cross-section, which were Example 3 subjected to the tests detailed below. I

For purposes of comparison, test pieces were made Poll/amide f q from of tel'cphthahl acld 1 f (a) a POD/amide pl-epamd as desgribgd above b 15 5% ISOphlhfillC acid and 3-isopropyl-hexamethylene (11- containing no stabilizer, (b) a polyarnide prepared as amine dscrlbed 111 Us. Patent d ibed above but containing only 0.9 part of O t stabilized with 0.25% of 061211111116, 0.04% of potassium mine and 0.33 part of phosphorous acid as stabilizers, i i and 1 506mm yp p i p The trans (c) a polyamide prepared as described above but con- Partial Clear polyamlde f p 111 9 f at 1400 taining only 0.9 part of Octamine as stabilizer, and (d) a 's alld'tfisled heat stiablllty as dfiscflbfid In E p polyamide prepared as described above but containing In test, t P l/ had suflelfid sllbstantlally 119 only 0.12 part of potassium iodide and 0.33 part of phoschange I t g and elongallon Seven phorous ,acid as stabilizefs weeks heating. IiljGClIlOl'l-ll'lOlClGCl plates 3 mm. thick, were The dumbbell test pieces were heated in an oven 61%? and y g y discolored (Y C QU after lhe through which air was circulated at 135 C. for 2 weeks, Seven Wefiks heatlflg, W'hefeflfi i116 unstflblllled P y or 1, 2, 3 or 4 months. They were then conditioned at turned j fi bTOWn dul'lflg the Same Period 1111661 The 20 C. and 100% relative humidity for 4-5 days before Sflme Conditions testing. After conditioning, the water content of the test What is l 151 pieces was about 1.5%. The tensile strength and elon- Al1 ?at-tfib1llZed liolyamlde 00111120311100 ll f f gation of the test pieces were measured (under standard d synthfilltl 11116111 amorphous. p y and slablhllllg conditions of 20 C. and percent relative humidity amounts an alkyl-substltllled dlphfllylflmme and the clamping jaws were moved with such speed that alkyl h g ffOm carbon atoms; Phosphorous break of the test piece occurred after 60 seconds) both comp Selected from the group 3 of 1 before and after the heat treatment. The results obtained PhOfOUS acid, a Salt of a Phosphorous acid: and an ester were as follows. The tensile strengths and elongations 35 of phosphorous acid; and a halide selected from the are expressed as a percentage of the value before the heat group consisting of hydrogen chloride, hydrogen brotreatmcnt. mide, hydrogen iodide, an alkali metal chloride, an alkali TABLE Properties after- 2 weeks 1 month 2 months 3 months 4 months Tensile Elon- Tensile Elon- Tensile Elon- Tensile Elon- Tensile Elon (01m strength gation strength gution strength gation strength gation strength gation lolyrnnide:

Unstabilizcd 26.5 7 Dark brown Containing Octamine and pl1os- 100 100 85 18 42 0 0 Light phorous acid. brown Containing Octaniino only 100 07 75 50 44 0 0 n Brown Containing potassium iodide and 30 25 10 7 0 0 ight phosphorous acid. yellow, Stabilized in accordance with this 100 100 100 100 100 100 100 75.5 20.3 l'fi g lilz invention, i.o., containing Octayellow mine, phosphorous acid and potus clear. slum iodide.

Oxygen absorption of the above described unstabilized metal bromide, an alkyl metal iodide, an alkaliearth and stabilized polyaniides was determined by an accelermetal chloride, an alkali earth metal bromide and an ated test in which the amount of oxygen reacting with the alkali earth metal iodide. sample was measured. A reaction vessel consisting of a I 2. A composition according to claim 11 wherein said curved tube with a ball-shaped end was connected to a 60 alkyl substituted diphenylamine is present in an amount U-tube containing mercury and sealed at one end. Soda of 0.1 to 1% by weight of the polyamide, said phoslime and. silica gel were used as absorbents for CO and phorous compound is present in an amount of 0.02 to H O. One gram of unstabilized polyaniide was placed in 1% by weight of the polyamide and said halide comthe bulb. The air in the apparatus was replaced by oxypound is present in an amount of 0.01 to 0.1% by weight gen by alternate evacuation and refilling with oxygen. of the polyamide.

The reaction vessel was placed in a sil'cone oil bath 3. A composition according to claim 1 wherein said heated to C. The oxygen uptake was measured alter alkyl-substituted diphenylamine is a member of the group 48 hours, and was 6.5 cm. per gram. The stabilized polyconsisting of di-t-butylphenylamine, di-neopentyldiphenamide according to this invention (i.e., containing Octap ylamine, di-isododecyldiphenylamine and the reaction mine, phosphorous acid and potassium iodide) had an product of diphenylamine and diisobutylene. oxygen uptake of only 1 cm. per gram. 4. A composition according to claim 1 wherein said Example 2 phosphorous compound is selected from the group consisting of phosphorous acid (H PO sodium phosphite,

Polyamide made from terephthalic acid and Z-ethyl- H sodium hyphosphite, potasium phosphite, potassium hy- 4-nicthylhexamethylene diamine (as tescribcd in US. phosphite, triethyl phosphite and triisooctyl phosphite.

5 0 5'. A composition according to claim 1 wherein said 2,530,769 11/1950 Hollis 26045.9 halide is a member of the group consisting of potassium 3,274,150 9/1966 Baevsky 260-45.9 1od1de, sodlum lochde and calclum lomue. FOREIGN PATENTS References Cite- 11 5 708,029 4/ 1954 Great Britain.

UNITED STATES PATENTS DONALD E. CZAJA, Primary Examiner.

3,160,597 12/1964 Costain et a1. 260-453 H. E. TAYLOR, Assistant Examiner. 

1. A HEAT-STABILIZED POLYAMIDE COMPOSITION COMPRISING A SYNTHETIC LINEAR AMORPHOUS POLYAMIDE AND STABILIZING AMOUNTS OF, AN ALKYL-SUBSTITUTED DIPHENYLAMINE SAID ALKYL HAVING FROM 4-12 CARBON ATOMS; A PHOSPHOROUS COMPOUND SELECTED FROM THE GROUP CONSISTING OF PHOSPHOROUS ACID, A SALT OF A PHOSPHOROUS ACID, AND AN ESTER OF PHOSPHOROUS ACID; AND A HALIDE SELECTED FROM THE GROUP CONSISTING OF HYDROGEN CHLORIDE, HYDROGEN BROMIDE, HYDROGEN IODIDE, AN ALKALI METAL CHLORIDE, AN ALKALI METAL BROMIDE, AN ALKYL METAL IODIDE, AN ALKALI-EARTH METAL CHLORIDE, AN ALKALI EARTH METAL BROMIDE AND AN ALKALI EARTH METAL IODIDE. 